Method for impregnating reinforcing fiber materials with a resinous binder material

ABSTRACT

Reinforcing fiber materials such as rovings, webbings, and other fiber materials are impregnated with a resinous binder material in such a manner that gaseous inclusions are avoided whereby a surprising increase in the strength of the fiber compound material is achieved. For this purpose the liquid resinous binder material is applied substantially only to one side of the reinforcing material which is then moved through an absorbing zone in which the liquid resinous binder material penetrates the reinforcing material substantially completely as a result of a predetermined residence time and temperature in the absorbing zone. Gas inclusions are removed by adsorption and/or by expulsion. The gas adsorbing and expulsion zone is a chamber in which a plurality of guide rollers are arranged so as to cause the impregnated material to repeatedly reverse its moving direction, whereby the sequential and repeated penetration of the reinforcing material by the resinous material and the removal of gas inclusions are enhanced. Further, the precise weight ratio adjustment of resin to fiber material is enhanced by moving the impregnated material in a substantially vertical orientation through a fulling station. The vertical orientation facilitates the flow off of excess resin.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.196,863, filed on Oct. 14, 1980 now abandoned. The parent application(U.S. Ser. No. 196,863) is based on German Patent Application No. P 2942 729.0, filed in the Federal Republic of Germany on Oct. 23, 1979. Thepriority of the German filing date is claimed for the presentcontinuation-in-part application through the parent application 196,863.

BACKGROUND OF THE INVENTION

The present invention relates to a method for impregnating reinforcingmaterials with a resinous binder material. The reinforcing materialsmay, for example, comprise fiber reinforcing materials such as rovings,fleeces, belts, cords, webbings or the like forming bands or strips.

The term "band" or "bands" will be used herein as a generic word for thewords listed. These bands of reinforcing materials are impregnated by aresinous binder agent for producing fiber compound materials, forexample for producing helicopter rotor blades. Conventionally, theresinous binder material is applied to one surface of the reinforcingmaterial.

Where fiber reinforced compound materials are used in the constructionof components which are subject to high dynamic wear and tear, it isnecessary not only to exclude air bubbles from the impregnated fibercompound material, but also to make sure that the adhesion of theimpregnating resin material on the entire surface of the reinforcingfiber material is complete. Spots of non-adhesion have been found tocause a rapid deterioration of the strength characteristic of helicopterrotor blades.

U.S. Pat. No. 3,762,364 (Funsch et al) discloses the coating ofsynthetic fiber webbings with an adhesive and with rubber for producingcar tires. The adhesive is applied to the advancing fabric sheet or beltas the latter is dipped into an adhesive dipping pan, whereby the fabricweb is coated with adhesive on both surfaces. Downstream of the dippingpan there is arranged a set of so-called hold-back rollers followed by adrying zone, a heat zone, and a normalizing zone forming together a hotstretching unit which in turn is followed by puller rollers. Downstreamof the puller rollers a fabric flexing unit is arranged which in turn isfollowed by the calendering unit for coating one surface of the fabricwith the rubber. The complete exclusion or avoidance of air inclusionsin the interstices between adjacent fiber threads is not essential inthe construction of pneumatic tires. Thus, in U.S. Pat. No. 3,762,364the flexing station actually increases the volume of the adhesive coatedfabric because the flexibility is more important than the totalavoidance of air inclusions. U.S. Pat. No. 3,762,364 refers tominimizing entrapped air pockets, however, such minimizing relates toair pockets between the metal beads of a tire building drum and the tirematerial prepared as described above.

In other conventional methods a paper web or a reinforcing material isguided over a rotatable impregnating roller dipping into a bath of theresinous binder material. U.S. Pat. No. 4,241,690 (Muller) isrepresentative of such coating. In such methods it is customary toadjust the ratio of the circumferential speed of the impregnating rollerto the feed advance speed of the reinforcing material or paper web inorder to vary the degree of application of binder material or othercoating material to the reinforcing material or other type of web.Excess resinous material may be stripped off, for example, by means ofdoctor blades or by means of squeezing rollers, please see also GermanPatent Publication (DE-AS) No. 2,012,107.

According to the prior art method it is possible to apply the bindermaterial in a single operation to the reinforcing material in aprecisely adjustable ratio between the binder material and thereinforcing material. This operation may be accomplished in the priorart method in a continuous manner. Nevertheless, the impregnationachievable according to the prior art is not optimal as far as 100%adhesion is concerned. Defects in the impregnation are especiallyapparent when rovings prepared according to known methods are used inthe so-called thimble or deadeye zone of the main rotor blades of ahelicopter. It has been found that the rovings suffer in the blade rootzone, which is subject to high loads, a premature shearing failurealready at relatively low load cycles. The failure occurs substantiallyspontaneously within a few thousand load cycles following the firstfailure indications. The separating break has the appearance of afailure due to tension loads of the glass fibers. However, the failureis actually due to shearing fractures or cracks and is believed to bedue to inadequate adhesion between the total available surface of thereinforcing material and the matrix formed by the impregnating resinousmaterial.

OBJECTS OF THE INVENTION

In view of the above it is the aim of the invention to achieve thefollowing objects singly or in combination:

to provide a method and apparatus for impregnating reinforcing materialssuch as fiber reinforcing materials in such a manner that the producedfiber compound materials will have a superior dynamic strengthcharacteristic;

to make sure that the resinous binder material completely penetratesthrough the interstices between the reinforcing material whilesimultaneously avoiding or eliminating gaseous inclusions even of thetiniest dimensions in the body of the fiber compound material to therebyassure a homogeneously impregnated fiber compound material;

to repeatedly subject the impregnated material prior to the curing ofthe resinous binder material to pressure on opposite sides or surfacesof the material to thereby enhance the penetration of the bindermaterial through the reinforcing material and to thereby drive out oradsorb and/or absorb gaseous inclusions;

to perform the homogeneous impregnation and gas removal or adsorptionand/or absorption under controlled temperature and residence timeconditions;

to assure a complete utilization of the available fiber surface of thereinforcing fibers for the adhesion of the resinous impregnatingmaterial to fibers,

to precisely adjust the ratio of the weight of the resinous impregnatingmaterial to the weight of the reinforcing fiber material forming a band;and

to provide a reinforced fiber compound material of a glass typetransparency as opposed to the whitish translucency of prior artso-called prepregs, whereby such transparent fiber compound material hasmuch improved material strength as compared to prior art prepregs.

SUMMARY OF THE INVENTION

The invention achieves the above objectives primarily in that thereinforcing material is transported substantially horizontally, afterthe application of the resinous binder material only to one surface ofthe reinforcing material, through an absorbing and adsorbing zone for apredetermined length of time while maintaining said absorbing andadsorbing zone at such a temperature that, in combination with thepredetermined length of time a substantially complete absorption of theresinous binder material by the fiber reinforcing material is assuredand so that any gaseous inclusions in the resinous binder material areeither driven out or adsorbed by the resinous binder material, wherebythe reinforcing fiber material is substantially completely saturated bythe liquid resinous binder material when the material leaves said zone.Thereafter the exact weight ratio of resinous binder material toreinforcing fiber material is adjusted in a fulling station throughwhich the material is advanced in a substantially vertical orientationwhich greatly facilitates said ratio adjustment because any excessresinous material may flow off easily due to the vertical orientation.

It has been found that by continuing the impregnation after theapplication of the resinous binder material to one side only, in anabsorbing and adsorbing zone under controlled conditions the resinousbinder material penetrates from the application side through thereinforcing material, whereby air inclusions are either pressedoutwardly or are adsorbed so that air inclusions are removed from thefiber compound material. In this manner it is possible to achieve ahomogeneously impregnated reinforcing material which does not have anyweak spots due to air or gaseous inclusions. This removal of air and gasinclusions takes place according to the invention in the resinousmaterial absorbing and adsorbing zone downstream of the applicationstation as viewed in the feed advance direction of the reinforcingmaterial. The substantially completely saturated reinforcing material isthen withdrawn from the absorbing and adsorbing zone and is transportedthrough a so-called fulling station in a substantially verticalorientation for removing any excess resinous material. If desired,further work stations may be arranged downstream of the fulling station.For example, one or more calibration nozzle stations and other treatmentor utilization stations may follow the fulling station.

The invention assures a perfect bond between the entire availablesurface of the reinforcing fibers and the impregnating liquid bindermaterial. This perfect bond is necessary for achieving the improvedstrength characteristics of the materials produced as taught herein. Dueto such perfect bond it becomes possible to transmit loads or rather theresulting stress from the resinous binder material into the reinforcingfibers to thereby fully utilize the strength characteristics of thesefibers. Thus, such bonding is critical for the overall strengthcharacteristics of the finished material.

It has been found that a plurality of factors influence the bondingbetween the fibers and the resinous binder material. Such factorsinclude the humidity, the interface surface tension between the fibersand the resin, the adsorption of any gas inclusion into the resin bodyor matrix, and especially the adsorption of moist air pockets at thebonding interface between fibers and the viscous resin. The exact ratioof the weight of the resin binder to the weight per unit of length ofthe fibers also influences the bonding strength. The present inventionmakes it possible to optimally satisfy all of these factors, but theadsorption of any gas bubbles or pocket at the surface of the fibers inthe resin and hence elimination of non-bonding zones between the fibersand the resin greatly increases the strength of the fiber compoundmaterial. Such strength is further enhanced by the exact weight ratioadjustment between resin and fibers.

The elimination of gas inclusions from interstices between fibers isaccomplished by the particular treatment in the application of the resinto the fibers. The exact weight ratio adjustment is possible by themovement of the impregnated fibers through the fulling station in avertical orientation.

A fiber compound material produced according to the invention, forexample, an impregnated roving, has a green, glass-type transparency.Contrary thereto a roving impregnated according to the prior art methodincludes entrapped air and hence has a whitish translucent appearance.When the material produced according to the invention is used tomanufacture main rotor blades for a helicopter in a laminating mold, ithas been found that the resulting rotor blades have a substantiallyhigher dynamic load characteristic than rotor blades made of the sametype of reinforcing rovings impregnated according to the prior art. Forexample, tests have shown that rotor blades made of the materialaccording to the invention do not show any load decrease even after morethan 5×10⁶ load cycles. Rotor blades tested under the same conditionsbut made of material impregnated according to the prior art exhibit loadfailures after a maximum of 0.02×10⁶ load cycles. This is considered tobe a non-predictable improvement.

Incidentally, the temperature in the resin absorbing zone is suitablymaintained by circulating heated air through the absorbing zone.

According to the invention an optimal impregnation of so-called endlessrovings is achieved in connection with warm or hot curing resin hardenersystems, especially of the epoxy resin type, by maintaining in the resinabsorbing zone a temperature in the range of 30° to 150° C. and assuringa residence or travel through time in this zone within the range of 30to 120 seconds.

For maintaining such a residence time or travelling through time thewithdrawing or travel speed should be within the range of 0.2 to 0.5m/s. The filament diameter of the reinforcing glass fiber material issuitably within the range of 5 to 15 microns, whereby the nontwistedglass silk rovings have a meter weight within the range of 600 to 2400tex, whereby 1 tex is equal to 1 gram per 1000 m length of roving.

The method according to the invention is advantageously performed in anapparatus in which the reinforcing material is guided over animpregnating roller or cylinder which dips into a bath of the resinousbinder material. The impregnating roller contacts but one side of thereinforcing material. Downstream of the impregnating station there isarranged a resin absorption zone through which the reinforcing materialis moved in a substantially horizontal orientation. Such zone isconstructed as a tower-type chamber in which guide rollers are arrangedin alternating succession at the top and bottom of the chamber, wherebythese guide rollers alternately reverse the travel direction of thematerial. The chamber is provided with heating and air blowing meanswhich as such are of conventional construction. Downstream of theabsorbing chamber there is arranged a guide arm which brings thematerial into a substantially vertical orientation for movement througha fulling station through which the material may be drawn with anadjustable speed. The vertical orientation of the material as it movesthrough the fulling station greatly facilitates the above mentionedweight ratio adjustment because the resin may flow off on both sides ofthe material. The air circulating means may comprise a blower whichdrives the air over heating coils for maintaining the desiredtemperature in the chamber.

Due to the bending of the impregnated material repeatedly in alternatedirections by the guide rollers in the absorbing chamber the intimateand complete penetration of the reinforcing material by the bindermaterial and the removal of air is enhanced.

BRIEF FIGURE DESCRIPTION

In order that the invention may be clearly understood, it will now bedescribed by way of example, with reference to the accompanyingdrawings, wherein:

FIG. 1 is a side view of an apparatus according to the invention forperforming the present production method;

FIG. 2 is a top plan view onto the apparatus of FIG. 1 substantially ina plane defined by section line II--II in FIG. 1; and

FIGS. 3 & 4 show on an enlarged scale relative to FIG. 1 the operationof the rollers in the treatment chamber.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BESTMODE OF THE INVENTION

Referring to FIGS. 1 and 2, the reinforcing fiber materials 1, forexample, comprising a plurality of glass rovings in the form of fiberbands 1 are guided in parallel to one another, but without contact. Thematerial is pulled off from a supply roller in a substantiallyhorizontal orientation, for example, by means of a pull-off device suchas a warp beam. A feed advance mechanism including a guide or lead-inroller 4 feeds the roving so as to travel substantially horizontallyinto contact with an impregnating roller 3 followed by a lead-out roller5 which feeds the rovings 1 into the absorbing and adsorbing treatmentchamber 6 past a lead-in roller 12 provided with longitudinal grooves12' extending in parallel to the longitudinal axis of the roller 12.These grooves 12' are preferably uniformly distributed about thecircumference of the lead-in roller 12 and also on the surface of theother guide rollers 11' in the chamber 6 for facilitating a smooth runof the reinforcing material by preventing the coiling of individualfibers or threads which have been separated from the rovings of thereinforcing material.

The impregnating roller 3 is rotatably supported in a trough 2 holdingthe resinous binder material. If desired, the roller 4 may be positivelydriven by conventional means such as an electric motor or the like. Inany event, the roller 3 coats only one surface of the fiber bands 1. Asthe roller 3 rotates, it transports by adhesion a desired quantity ofresinous binder material for application to the underside or surface Aof the reinforcing material 1 running over the roller 3, whereby thematerial 1 entrains the resinous material and takes it along into thetower-type treatment chamber 6. The bands 1 are referred to by reference1' downstream of the roller 3 as viewed in the feed advance directionfrom right to left.

Although the inlet roller 12 is shown to be arranged at the bottom ofthe chamber 6, it may also be arranged at the top or intermediate theends of the chamber 6. However, the inlet roller 12 will be positionedto contact the fiber bands 1' on the side or surface B which is oppositeto the coated side A as shown in FIG. 1. Similar considerations applyfor the outlet guide roller. Between the inlet and outlet rollers, theguide rollers 11 and 11' are arranged in alternate succession onopposite sides A, B of the bands 1' so that the direction of movement ofthe reinforcing material bands 1' is repeatedly reversed prior to itsexit from the chamber 6, whereby the complete penetration of thereinforcing material by the binder material and the removal of air fromthe fiber compound material is enhanced as will be described in moredetail below with reference to FIGS. 3 and 4. The feed advance directionis indicated by the arrow 10. The number of guide rollers 11, 11' whichmay be arranged in the manner of a calender, is selected in such a way,depending on the feed advance speed of the material 1, that the desiredresidence or travel through time in the chamber 6 is achieved.

A guide wall 8 is arranged in the chamber 6 for guiding an airstreamindicated by the arrows 9 inside the chamber 6. The airstream isproduced by a heater blower device 7 of conventional construction tokeep the air circulating inside the chamber 6. The air is heated to suchan extent that inside the chamber a desired temperature is maintained ata substantially constant level. The temperature is selected so as toassure the desired viscosity of the resinous binder material applied tothe material 1' so that the binder material may penetrate through or"sweat" through the reinforcing material from the side A to which it hasbeen applied to the opposite side B. This penetration or sweatingthrough is even enhanced by the operation of the reversing rollers 11,11' and 12 because these rollers are so positioned that alternaterollers contact opposite surfaces of the reinforcing material bands 1.

In addition to the above mentioned function of the grooves 12' in therollers 12 and 11, 11' of preventing a coiling of individual filamentsof the reinforcing material 1', these grooves also provide receptaclesfor excess binder material, thereby assuring a smooth run of thereinforcing material 1' over the rollers 11, 11' and 12.

A receptacle 13 receives excess resinous binder material dripping downfrom the roller ends out of the grooves 12' and also dripping off thereinforcing material 1'.

Downstream of the tower-type chamber 6 there is arranged a guide arm 16which guides all the bands or rovings 1' out of a substantiallyhorizontal orientation into a substantially vertical orientation fortravel through a fulling station 14 in which any remaining excessresinous material is stripped off the reinforcing and now impregnatedmaterial 1. Downstream of the fulling station 14 there is preferablyarranged a further guide arm 18 and a calibration device 15 and otherworking or utilization stations not shown.

The fulling station 14 comprises a trough 14' in which any excess resinmaterial is collected. Upper and lower vertically extending fulling pins17 are adjustable relative to each other as indicated by the doublearrows 23 in FIG. 2. The adjustment means for the fulling pins 17 arenot shown since they are conventional. By adjusting the position of thefulling pins 17 in combination with the substantially verticalorientation of the bands 1' in the fulling station the inventionprovides a means for very precisely controlling the weight ratio ofresin material to fiber material per unit of length. Adjustments asprecise as ±0.03% of a given weight ratio have been made. This precisionis very important for achieving the desired material strength of thefinished product made of the resulting fiber compound material.

The further guide arm 18 downstream of the fulling station 14 preferablybrings the impregnated fibers back into a substantially horizontalorientation for horizontal feeding into the calibration device 15 whichcombines, for example 18, bands, strands, or rovings, into a singlesheet of fiber compound material having the required width horizontallyand the required thickness vertically when leaving the calibrationdevice 15.

The reinforcing material may preferably be selected in the form ofrovings made of glass fibers, carbon fibers, or fibers of aromaticpolyamides.

The following examples further illustrate the invention.

EXAMPLE 1

Eighteen rovings made of nontwisted glass silk monofilaments having adiameter of 9 microns are assembled to form a so-called warp beamcharge. These glass silk monofilaments are known under the typedesignation EC 9-756-K 43/68 HF, Code 6805.

These filaments forming the reinforcing fibers have a temperature of 50°to 60° C. and are held in an atmosphere having a relative humidity of 40to 70%. The rovings pulled off the warp beam run individually over animpregnating cylinder 3 dipping into a bath of resinous binder materialcontained in a trough 2. The resin is in this example a condensationproduct of epichlorohydrin and 4,4 -Diphenylolpropane which is free ofany additives such as solvents, thinners, and so forth. The chemicalbasis for the hardener is 4,4 -Diaminodiphenylmethane. The mixing ratioof resin to hardener is 100:27 parts by weight. The bath temperature isin the range from 49° to 50° C. The viscosity of the resin hardenersystem in the bath is within the range of 200 to 500 mPas.

The impregnating roller 3 carries out of the bath a resinhardener filmhaving a defined thickness. This film impregnates the glass rovings onthe contact side A where the rovings 1 contact the impregnating rolleror cylinder 3. The excess resin of the impregnated rovings 1' downstreamof the roller or cylinder 3 is within the range of 20 to 40% by weight.The rovings 1' coated on one side only are introduced into the chamber 6with a feed advance speed of 13 m/s. In the chamber 6, as shown in thedrawing, seven guide rollers 11, 11' are arranged as mentioned above.The degree of saturation of the resin hardener system at the entrance ofthe chamber 6 is still within the range of 120 to 140%. In the chamber 6the individual rovings forming the coated reinforcing material 1' areguided one next to the other so that the resin may penetrate or sweatthrough the respective rovings from the coated side A to the oppositeside B. Due to the increased temperature in the chamber 6 which ismaintained within the range of 50° to 60° C. and due to the constantfeed advance speed the material exchange is optimally facilitated. Theheated air which is circulated to maintain a constant temperaturethroughout the volume of the chamber 6 is a dry air in order to keepgases in solution in the resin binder.

The vertical spacing between a lower guide roller 11 and an upper guideroller 11' is about 1.5 m to 2 m. The diameter of the guide rollers 11is about 120 mm. The grooves 12' extending in parallel to thelongitudinal roller axis in the entrance roller 12 and in the guideroller 11, 11' have a depth and a width of 4 mm each. The entire lengthof the rovings within the chamber 6 is about 10 m so that the residenceor travel through time is within the range of 45 to 50 seconds. Theimpregnation is completed when the rovings 1' exit from the chamber 6.About 0.5 m downstream of the chamber 6 there is located the abovementioned fulling station 14 for adjusting the exact resin proportionafter guiding the rovings out of a substantially horizontal orientationinto a substantially vertical orientation by means of the guide arm 16.If it is desired, for example, to obtain a glass to resin weightproportion of 73.4% by weight of the total weight, then it is necessaryto provide a resin volume proportion of 42%. Any excess resin materialremoved in the fulling station 14, for example, by means of the verticalfulling pins 17 in the form of blades or rollers, is collected in achamber 14' and returned into the trough 2.

About 0.5 m downstream of the fulling station 14 there is arranged acalibration nozzle 15 for achieving the desired belt cross-section of0.8×20 mm. The calibration nozzle or device 15 is not shown in detailsince it is not part of the invention. The further guide arm 18 betweenthe fulling station 14 and the calibration device 15 may be used forfeeding the impregnated rovings 1' horizontally into the device 15. Thecalibrated roving belts are pulled off in lengths of 10 m and severed.At this time a piece of roving having a length of 20 cm is cut off andplaced on a precision scale for weighing. Depending on the weighingresult the fulling pins or rollers are manually adjusted so as to inturn adjust the ratio beween resin and roving material as precisely asdown to ±0.03 per thousand (.permill.) of a given weight ratio.

A roving produced in the manner described above has a glass typetransparency and is placed into one half of a laminating mold formanufacturing a rotor blade. The roving is massaged, for example, with aspatula so that it assumes the contours of the mold. The roving retainsits greenish transparency. It has been found that rotor bladesmanufactured as described may be exposed dynamically to load cycles upto 5×10⁶ without the occurence of any defects. On the other hand, rotorblades made of rovings impregnated according to the prior art showdefects with certainty if load cycles of 0.02×10⁶ are reached. It hasfurther been found that differences in the pulling speed or in thetravel through speed of the reinforcing material 1 through the chamber 6do not have a disadvantageous influence on the optimal impregnation. Onthe other hand, according to prior art impregnating methods it isnecessary to maintain precisely the pulling off speed.

EXAMPLE 2

For producing a roving belt of an aromatic polyamide fiber with apolyurethane resin matrix to manufacture a tension element, coils ofaromatic polyamide fibers such as are known under the trade name Kevlar49 manufactured by DuPont are assembled to form a warp beam charge. Theyarn of the just mentioned type has a Denier value of 1420 and is notprovided with any means for enhancing the adhesiveness. The polyamidefiber or yarn coils are maintained, prior to their use, for ten hours inan environment having a relative humidity of 10 to 30% and having atemperature in the range of 110° to 130° C. These yarns are not twistedand are pulled off the warp beam whereupon they run, as in Example 1,over the impregnating roller or cylinder 3. The resinous bath comprisesa polyurethane resin hardener system having a viscosity in the range of100 to 150 mPas at a temperature between 25° and 30° C. This type ofresin is a diisocyanate. In order to avoid exothermic reactions thetotal quantity of resin does not exceed 1 kilogram.

The polyamide fiber yarn travels through the chamber 6, the internaltemperature of which is kept within the range of 30°±2° C. The otherfeatures or steps correspond to those of Example 1. The resulting rovingbelt has a homogeneous, optimal resin impregnation which issubstantially free of any air inclusions due to mechanical squeezing outof air bubbles and due to adsorption of any remaining gas inclusions inthe resin.

A tension element made of roving belts impregnated as just described,may be subjected to very high tension loads.

EXAMPLE 3

Ten coils of a high strength carbon fiber of the type T 300 6K made byToray in Japan are assembled to form a warp beam charge. Thecross-section of a fiber bundle is 0.2 mm². The carbon fiber coils onthe warp beam are maintained for five hours at a temperature of 90° C.to 100° C. and at a relative humidity within the range of 30 to 50%. Thecarbon fiber yarns which are not twisted are then pulled off the warpbeam and guided over the impregnating roller or cylinder 3. The trough 2holds a polyamide resin of the type H 353 made by Technochemie ofDuessenheim, West Germany. The resinous binder material in the trough 2is maintained at a temperature within the range of 125° to 130° C. Inorder to keep the thermosetting single component resin in liquid form,or rather in solution, it is necessary that all guiding elements androllers are preheated. The resin is very viscous. The kinematicviscosity is within the range of 1 to 1.5 cm² /s Such viscosity ismaintained during the time of working the material. The carbon fibersare guided through the chamber 6 in the same manner as the roving fibersdescribed in Example 1, whereby the temperature in the chamber 6 ismaintained by air circulation having a temperature within the range of140° to 160° C. The rollers 11 and 12 are maintained at a temperature inthe range of 125° to 130° C. A complete penetration of the carbon fiberyarns by the resin is accomplished to the exclusion and adsorption ofsubstantially all entrapped air bubbles. In order to compensate for anyheat losses infrared radiating heaters may be arranged upstream anddownstream of the chamber 6 as viewed in the feed advance direction ofthe carbon fibers. The roving belts produced according to Example 3 areespecially suitable for manufacturing so-called "advanced rotor blades"and for making turbine blades or vanes.

EXAMPLE 4

This example relates to the impregnating of a belt of glass webbing forthe manufacture of the covering skins of longitudinal structuralcomponents having a defined torsion stiffness. For this purpose a glasssilk webbing coil is used having a width corresponding to the width ofthe structural component. In order to increase the torsion stiffness aspecial kind of webbing is used in which the glass fibers are orientedat ±45° relative to the pull off or travel direction of the webbing. Inthis type of webbing the glass fibers oriented in different directionsmay either by tied to one another to a certain extent or they may bemerely connected by binding threads without any tying, whereby onethread rests on another. The area or surface weight of such a glass silkwebbing may be within the range of 50 to 500 g/m².

The coil or spool of glass webbing is preheated to 60° C. in anenvironment having a relative humidity within the range of 50 to 70%.All other treatment parameters are the same as set forth above inExample 1.

The belt of glass webbings is transported through the entireimpregnating and absorbing chamber 6 in the same manner as the rovings.However, it is to be noted that by using a webbing with fibers orthreads running in directions at ±45°, it is necessary that threads mustalso be arranged in the pulling off direction to avoid the so-called"cravat effect". All types of webbings may be pulled through the chamber6 in the warp direction or in the weft direction for the impregnation.

After the webbing belt has left the chamber 6 the impregnation iscompleted. Downstream of the chamber 6 the layer of the impregnatedwebbing belt is tilted through about 90° by means of the guide arms 16and, if desired also 18 downstream of the fulling station 14.Approximately 1 m downstream of the chamber 6 a fulling station isarranged for adjusting the desired resin content in an exact manner. Inthis connection it is also important that the removal of any excessresin hardener proportion is carried out only after completion of theimpregnating.

According to the invention it is possible to impregnate webbings havingthe following advantages. The impregnated webbing according to theinvention has a glass type transparent appearance. Contrary thereto, awebbing prepreg according to the prior art has a whitish translucencywhich appears to be due to an insufficient or faulty impregnationresulting in air inclusions and inadequate bonding. The disadvantages ofsuch faulty impregnation are mainly due to the mechanicalcharacteristics of the resulting products. According to the invention itis easily achieved to satisfy a rated glass weight proportion of about50% and to precisely maintain that proportion at a constant level.Another advantage is seen in that for the construction of blade skinsthe labor costs are substantially reduced as compared to prior artmanual impregnating methods.

FIGS. 3 and 4 illustrate on an enlarged scale compared to FIG. 1, thefunction of the rollers 11 and 11'. An upper roller 11' is shown in FIG.3 and rotates counterclockwise as indicated by the arrow 21, in contactwith the surface A of a band or roving 1'. The surface A has just beencoated with resin while running over the roller 3. Due to the pull ofthe roller 11' in contact with the resin coated surface A of the band 1'the resin is pressed in the direction 19 through any interstices betweenadjacent fibers toward the surface B of a band 1. In FIG. 4 the surfaceB comes into contact with the next, clockwise rotating lower roller 11.Arrow 22 indicates the rotation direction. Now the resin is pressedthrough any interstices or spaces as indicated by the arrows 20 fromsurface B to surface A. Thus, the resin is caused to repeatedly andsequentially travel from surface A to surface B and vice versa as itpasses through the treatment chamber 6. This travel has been compared toa "sweating through", whereby gas inclusions in the interstices orspaces between fibers are substantially completely eliminated either bybeing pressed out of interstices or spaces or adsorbed into the resinmaterial. Such elimination of gas inclusions has greatly increased thematerial strength of fiber compound materials produced as taught herein.

Although the invention has been described with reference to specificexample embodiments, it will be appreciated, that it is intended tocover all modifications and equivalents within the scope of the appendedclaims.

What is claimed is:
 1. A method for producing fiber compound materialmade of bands of reinforcing fiber material impregnated with a liquidresinous binder, comprising the following steps:(a) using as saidreinforcing fiber material a fiber material having a meter weight up toabout 2400 tex and a diameter of about 5 to 15 microns for each fiber,and using as said liquid resinous binder a warm or hot curing resinhardener system, (b) advancing a plurality of said bands of reinforcingfiber material in parallel to one another and substantially horizontallyover an impregnating roller (3) so that only one surface (A) of eachband (1) contacts the impregnating roller for coating said one surfaceof the bands with an excess quantity of said liquid resinous binder,said excess quantity being in excess of a quantity required for completeimpregnation, (c) advancing said bands for at least 30 seconds over aplurality of rollers (11, 11') forming a calender type rollerarrangement in a temperature controlled chamber (6) for sequentially andrepeatedly applying pressure alternately to opposite surfaces of a bandof reinforcing fiber material, to completely and repeatedly penetratesaid bands with said liquid resinous binder by the action of saidrollers for eliminating gas bubbles from interstices between fiberswhile circulating heated air in said temperature controlled chamber (6),while maintaining a temperature in said chamber within the range ofabout 30° C. to about 150° C., (d) guiding the completely penetratedbands outside said chamber (6) from a substantially horizontal advanceinto a substantially vertical advance, and (e) moving the completelypenetrated advancing bands through a fulling station (14) for adjustingthe quantity of liquid resinous binder in the bands relative to thequantity of fiber material to form fully impregnated bands.
 2. Themethod of claim 1, wherein as said reinforcing fiber material glass silkrovings are used having a meter weight in the range of 600 to 2400 texand wherein the time for passing through said temperature controlledchamber (6) is 30 to 120 seconds.
 3. The method of claim 1 or 2, whereinsaid excess quantity of liquid resinous binder corresponds to 20 to 40%by weight of a quantity required for complete impregnation.
 4. Themethod of claim 1 or 2, further comprising arranging rollers of saidcalender type roller arrangement in said temperature controlled chamberin such positions that first inlet roller means (12) contact said bandson the surface (B) opposite said one surface (A) coated with said liquidresinous binder for first bending said bands so that the coated surfaceis first on the outside curve of the respective bend, and so thatfurther quide rollers contact the bands alternately on the respectiveopposite surface for bending the bands in alternately oppositedirections for said sequentially and repeatedly applying pressure to thebands.
 5. The method of claim 1, further comprising guiding thecompletely impregnated bands downstream of said fulling station (14)back into a substantially horizontal advance for moving the fullyimpregnated bands substantially horizontally into a calibration means(15) for achieving a desired cross-section of the fiber compoundmaterial.
 6. The method of claim 1, wherein gas bubbles in intersticesbetween fibers of the fiber material are absorbed into the liquidresinous binder.
 7. The method of claim 1, further comprising using assaid calender type rollers at least one calender type roller withlongitudinal grooves in the roller surface, which grooves extendsubstantially in parallel to a longitudinal roller axis, for smoothlyadvancing said bands.